No 35, Reports Oceanography

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Temporal and spatial distribution

of diarrhetic shellfish toxins in blue

mussels,

Mytilus edulis

(L.), on the

Swedish west coast, NE Atlantic,

1988-2005

Bengt Karlson, Ann-Sofi Rehnstam-Holm & Lars-Ove Loo

Reports Oceanography

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Bengt Karlson, Ann-Sofi Rehnstam-Holm & Lars-Ove Loo

Temporal and spatial distribution of diarrhetic shellfish toxins in blue mussels, Mytilus edulis (L.), on the Swedish west coast, NE Atlantic, 1988-2005. Swedish Meteorological and Hydrological Instute, Reports. Swedish Meteorological and Hydrological Instute, Reports Oceanography, no 35, 40 pp.

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Temporal and spatial distribution of diarrhetic shellfish tox

-ins in blue mussels,

Mytilus edulis

(L.), on the Swedish west

coast, NE Atlantic, 1988-2005

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Swedish Meteorological and Hydrological Institute S-601 76 Norrköping Sweden RO No. 35 Report date/utgivningsdatum 2007 Author (s)/Författare

Bengt Karlson, Ann-Sofi Rehnstam-Holm & Lars-Ove Loo

Title (and Subtitle)/Titel

Temporal and spatial distribution of diarrhetic shellfish toxins in blue mussels, Mytilus edulis (L.), on the Swedish west coast, NE Atlantic, 1988-2005..

Abstract/sammandrag

The main goal of this report is to compile and present available data on algal toxins in blue mussels from the west coast of Sweden. The hazards associated with the consumption of mussels are mostly dependent on the occurrence and composition of toxic algae in the areas where shellfish are grown. Diarrhetic shellfish toxins (DST), i.e. okadaic acid (OA) and dinophysistoxin-1 (DTX-1) have occurred regularly in blue mussels (Mytilus edulis) at the Swedish west coast (i.e. Skagerrak) during the past years. A maximum residue limit of 160 µg.kg-1_{mussel meat has been set}

by National Food Administration. The toxic incidences in the region has been linked to the occurrence of Dinophy-sis acuminata and D. acuta. In general there is seasonal variation of DST in mussels with low concentrations from March to August (<160 µg.kg-1_{mussel meat) and high from October to December (>160 µg.kg}-1_{mussel meat).}

Peaks above the maximum residue limit have in some years also occurred in late June to late July. Rapid intoxica-tion vs. slow detoxificaintoxica-tion of mussels is a common phenomenon, especially in autumn-winter. Temporal and re-gional differences are large. There is also a considerable variation in toxin levels between years. In 1994 almost 5000 µg DST.kg-1_{mussel meat was detected. In 1997 mussel farmers experienced very low levels, i.e. only three samples}

above the restriction limit of DST. In autumn 1989 to spring 1990 and in early autumn 2000 to early 2001, high levels (about 200 to 2000 µg DTX.kg-1_{mussel meat) were recorded during 26 weeks. The Koljö Fjord region had}

low levels of toxins until 1998, despite regular recordings of potentially DST producing algae in the area. Today mussels grown and harvested in this area have similar toxin levels to mussels from other fjords in the Skagerrak region. Measurements of other toxins than DST are few and are not included in the report.

Key words/sök-, nyckelord

Dinophysis, Harmful algal bloom, Kattegat, Skagerrak, marine, DSP, toxins, Mytilus edulis, Blue mussel, Common mussel

Supplementary notes/Tillägg

Summaries in both Swedish and English are found in the report

Number of pages/Antal sidor

40

Language/Språk

English

ISSN and title/ISSN och titel

ISSN 0283-11112 SMHI Reports Oceanography

Report available from/Rapporten kan köpas från:

SMHI

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Summary in Swedish/Svensk sammanfattning

1 Summary

1 Preface

2 1 Introduction

3

1.1 Description of the area 3

1.2 Aquaculture – short description and history 3

1.3 Algal blooms 4

2 Material & methods

8

2.1 Description of collected data 8

2.2 Analysis methods 8

3 Results

9

3.1 Collected data 9

3.2 Occurrence of Dinophysis spp. and its correlation to toxicity in mussels 9

3.3 Temporal and spatial distribution of total DST 9

3.4 Kosterfjorden 10 3.5 Tjärnö archipelago 11 3.6 Rossö-Resö archipelago 12 3.7 Sannäsfjorden 13 3.8 Fjällbacka archipelago 14 3.9 Sotefjorden 15 3.10 Gullmarns centralbassäng 16 3.11 Malö strömmar 17 3.12 Koljö fjord 18 3.13 Borgilefjorden 19 3.14 Kalvöfjord 20 3.15 Havstensfjorden 21 3.16 Ljungskile 22 3.17 Käringöfjorden 23 3.18 Mollöfjorden 24 3.19 Lyresund 25 3.20 Boxvike kile 26 3.21 Halsefjorden 27 3.22 Stigfjorden 28 3.23 Kalvöfjorden 29 3.24 Marstrandsfjorden 30 3.25 Göteborgs s skärgårds kustvatten 31 3.26 Askims fjord 32 3.27 N m Hallands kustvatten 33

4 Discussion

34

5 Conclusion

35

6 References

36

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Summary in Swedish/Svensk sammanfattning

Målet med denna rapport är att sammanställa och presentera tillgängliga data med algtoxiner i blåmusslor från svenska västkusten. Risken att bli förgiftad av algtoxiner via musslor hänger samman med förekomst och sammansättning av toxiska alger i det vatten där musslorna växer. Diarréframkallande ämnen (diarrheic shellfish toxins), t.ex. okadasyra (OA) och dinophysistoxin-1 (DTX-1) har förkommit regelbundet i blåmus-slor (Mytilus edulis) längs svenska västkusten (Skagerack) de senaste tjugofyra åren. Ett gränsvärde på 160 µg.kg-1_{musselkött är fastställt av livmedelsverket. Toxinförekomsten i regionen associeras till förekomsten av}

Dinophysis acuminata och D. acuta. “Normalt” är det en säsongsvariation av DST i musslor med låga koncen-trationer från mars till augusti (<160 µg.kg-1_{musselkött) och höga från oktober till december (>160 µg.kg}-1

musselkött). Toppar över gränsvärdet för konsumtion har vissa år förekommit från slutet av juni till slutet av juli. En snabb ökning i toxinhalt respektive långsam minskning är också ett vanligt förekommande fenomen, speciellt under höst-vinter. Tidsmässiga och regionala skillnader är stora. Det är också en stor skillnad i tox-inhalt mellan åren. 1994 uppmättes den högsta toxtox-inhalten till nästan 5000 µg DST.kg-1_{musselkött. Under}

1997 var halterna låga under hela säsongen, endast vid tre tillfällen var halterna över gränsvärdet. Från hösten 1989 till våren 1990 och från tidig höst 2000 till tidig vår 2001 uppmättes höga halter (ca 200 to 2000 µg DTX.kg-1_{musselkött) under 26 veckor i en följd. I Koljöfjorden var det låga halter av toxiner fram till år}

1998, trots förekomst av potentiellt DST producerande alger i området. I dag har musslor som växer och skördas i detta område ungefär samma nivåer av toxin som från andra områden. Mätningar av andra algtox-iner än DST är fåtaliga och tas inte upp i rapporten.

Summary

The main goal of this report is to compile and present available data on algal toxins in blue mussels from the west coast of Sweden. The hazards associated with the consumption of mussels are mostly dependent on the occurrence and composition of toxic algae in the areas where shellfish are grown. Diarrhetic shellfish tox-ins (DST), i.e. okadaic acid (OA) and dinophysistoxin-1 (DTX-1) have occurred regularly in blue mussels (Mytilus edulis) at the Swedish west coast (i.e. Skagerrak) during the past years. A maximum residue limit of 160 µg.kg-1_{mussel meat has been set by National Food Administration. The toxic incidences in the region}

has been linked to the occurrence of Dinophysis acuminata and D. acuta. In general there is seasonal variation of DST in mussels with concentrations low from March to August (<160 µg.kg-1_{mussel meat) and high from}

October to December (>160 µg.kg-1_{mussel meat). Peaks above the maximum residue limit have in some}

years also occurred in late June to late July. Rapid intoxication vs. slow detoxification of mussels is a common phenomenon, especially in autumn-winter. Temporal and regional differences are large. There is also a con-siderable variation in toxin levels between years. In 1994 almost 5000 µg DST.kg-1_{mussel meat was detected.}

In 1997 mussel farmers experienced very low levels, i.e. only three samples above the restriction limit of DST. In autumn 1989 to spring 1990 and in early autumn 2000 to early 2001, high levels (about 200 to 2000 µg DTX.kg-1_{mussel meat) were recorded during 26 weeks. The Koljö Fjord region had low levels of toxins until}

1998, despite regular recordings of potentially DST producing algae in the area. Today mussels grown and harvested in this area have similar toxin levels to mussels from other fjords in the Skagerrak region. Measure-ments of other toxins than DST are few and are not included in the report.

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Preface

Regular monitoring of diarrhetic shellfish toxins in blue mussels using chemical methods started in 1988. Several people and institutes have been involved in sampling and analysis and without their effort it would not have been possible to produce this report. One of the pioneers was Professor Lars Edebo at the Sahlgren-ska University Hospital in Göteborg. The Department for Medical Microbiology at SahlgrenSahlgren-ska continued the routine analysis in 2000. Since then the National Food Administration has commissioned the private company AnalyCen AB in Lidköping for the analyses. The mussel farmers, the Water Quality Association of the Bohus Coast, the National Food Administration, several research projects and others have contributed to the funding for sampling and analyses. Staff at SMHI have aided in compiling the data in a structured format from raw data available in various formats. All the effort involved in producing the data presented in this report is greatly acknowledged. This work was initiated after trying to summarize the algal toxin situation for a report for the Oslo-Paris commission (Karlson and Rehnstam-Holm, 2002) and some of the work was car-ried out as part of the EU project HABES (Harmful Algal Bloom Expert System) contract EVK2-CT-2000-00092.

The report was produced in co-operation, by the Oceanographic unit in Göteborg, Swedish Meteorological and Hydrological Insitute, the Institution of Marine Ecology, Tjärnö Marine Biological Laboratory, Göteborg University and the University of Kristianstad.

Bengt Karlson February 2007

Authors addresses

Dr. Ann-Sofi Rehnstam-Holm. Göteborg University, Clinical Bacteriology, Institution of Laboratory Medi-cine, SE-413 46 Gothenburg, Sweden & Kristianstad University, Institution of Mathematics and Natural Sciences, SE-29188 Kristianstad, Sweden.

Dr. Bengt Karlson. Swedish Meteorological and Hydrological Institute, Oceanographic Services, Nya Varvet 31, SE-426 71 Västra Frölunda, Sweden.

Dr. Lars–Ove Loo. Department of Marine Ecology, Göteborg University, Tjärnö Marine Biological Labora-tory, SE-452 96 Strömstad, Sweden.

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Figure 1. The arrows shows the dominating cur-rent pattern in Skagerrak and Kattegat above the halocline.

1 Introduction

1.1 Description of the area

Mussel farms along the Swedish west coast are situated in fjords or in the archipelago along the eastern boundaries of the Kattegat and the Skager-rak in the North East Atlantic. One characteristic of the area is that the tidal amplitude is less than 30 cm. The Kattegat surface water is strongly influenced by the outflow of brackish water from the Baltic that forms a surface layer with a salinity of ca 15 ‰ in the Southern part. Surface salinity increases northward along the coast to ca 25 ‰ in the North-eastern Skagerrak. Water originating from the North Sea is found below a pronounced halocline at a depth of about 15 m. The salinity in the deep water range from 32 to 34 ‰. The Kattegat and the Skagerrak have surface areas of about 22 000 and 32 000 km2_{and mean depths of}

23 m and 210 m, respectively. In the fjords along the coast local conditions such as sills and freshwa-ter input from rivers change the general patfreshwa-tern. Anthropogenic input of nutrients has resulted in eutrophication in several areas. Oxygen depletion in the Kattegat is a common event in autumn and some of the fjords have more or less permanent oxygen depleted deep water.

1.2 Aquaculture – short description and history

Blue mussels (Mytilus edulis) are important filter feeders in Swedish coastal waters and long-line blue mussel culturing systems have been in common use in Skagerrak since the early 1980s (Ackefors & Haamer 1987). The first mussel cultures were introduced to the area in 1971 (Loo & Rosenberg 1983). The mussels are grown on hanging, 6-meter suspenders attached to horizontal lines. Normally

’��’ ��’ ��’ ��’ ��’ ��’ ��’ ��’ ��’ ��’ ��’� ��’��’ ��’��’�� ’��’ ��’ ��’ ��’ �� ’ ��’ ��’ ��’ ��’ ��’ ��’ ��’ �� ’�� ’ ��’ �� ’�� ’ ��’ �’ �� ’ �� ’ ��’ �� ’ �� ’ �� ’ �� ’ �� ’ �� ’ �� ’ �� ’ �� ’ �� ’ �� ’��’ ��’ ��’ ��’ ��’ ��’ �� ’�� ’ ��’ ��’ �� /SLO 'ÚTEBORG +BENHAVN

3KAGERR

AK

+ATT

EGAT

the larvae settlement occurs abundantly in June (about 2500–10000 ind..m-1_{suspenders) along the}

Skagerrak coast. The gross production capacity of an average Swedish long-line unit is 140 to 200 tonnes of mussels in 18 months (Loo & Rosen-berg, Haamer 1995). Each long-line unit occupies a water surface area of about 2000 m2_{and acts as}

a large three-dimensional bio-filter (10 x 200 m, ~8 m deep). An optimal site on the Swedish West

Figure 2. Swedish long-line culture from the surface on the picture to the right and under water on the left pic-ture. Photo Lars-Ove Loo.

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Coast can produce up to 40 kg of fresh mussels per m2_{and year, filtering off the phytoplankton}

biomass produced by about 25 m2_{of sea surface}

(Haamer, 1995).

1.3 Algal blooms

High biomass blooms

Algal blooms are common and, in general, natural phenomena in the area. In the end of February or in March the diatom spring bloom usually occurs. The biomass of phytoplankton usually reaches the yearly peak during the spring bloom and since

zooplankton such as copepods grow slower than the diatoms a large part of the spring bloom ends up on the sea floor where filter feeders and other benthic animals utilize this resource. Diatoms, dinoflagellates and other flagellates often form blooms during the rest of the growing season but biomass is in general lower since zooplankton feed on the blooms. In May-June blooms of flagellates harmful to fish and other organisms have occurred in several years. In 1988 Chrysochromulina polylepis, formed a devastating bloom. Chattonella cf. verru-culosa (proposed new name Verrucophora verruculo-sa) caused fish kills in 1998 and also bloomed in 2000, 2001, 2004 and 2006. The coccolithophorid Emiliania huxleyi has formed spectacular blooms in the North Sea-Skagerrak area in May-June in several years. In 2004 the bloom reached the Bohus coast and the water was discoloured turquoise from

Figure 3. A schematic drawing of a Swedish long-line culture (After Haamer, 1995).

Figure 4. Blue mussels growing on polypropylene suspenders in a mussel culture. Photo Lars-Ove Loo.

Figure 5. Dinophysis acuta (left) and D. norvegica (right). Photo Mats Kuylenstierna.

Figure 6. Dinophysis acuminata (left) and Phalachroma rotundatum (right). Photo Mats Kuylenstierna.

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the calcite plates covering the algal cells. This alga is harmless. During summer really small cyanobac-teria (1/1000 mm in diameter) dominate produc-tion but biomass is in general low. Diatom blooms are common in autumn.

Blooms of the diatom genus Pseudonitzschia fre-quently occur in the Skagerrak and the Kattegat (Karlson et al. 2005). Several species from this ge-nus produce domoic acid and cause Amnesic Shell-fish Poisoning (ASP). The toxin has been detected in shellfish in Denmark and Norway. In Denmark levels above the regulatory limit were detected in 2004. The dataset on Amnesic Shellfish Toxins (AST) in blue mussels in Sweden is very small and has not been included in this report.

Low biomass blooms causing shellfish

toxicity

The most important harmful algae for mussel harvesting occur in low cell numbers and do not form high biomass blooms. Along the Swedish West coast the most potent toxins are produced by dinoflagellates belonging to the genus Alexandrium. Some of these produce Paralytic Shellfish Toxins (PST) causing Paralytic Shellfish Poisoning (PSP), which can lead to death. Alexandrium spp occur regularly along the Bohus coast, most often in late spring (Karlson et al. 2005). The dataset on PST in blue mussels is too small to be included in the present report. Other toxin producing

dinoflagel-lates include Lingulodinium polyedrum and Proto-ceratium reticulatum. These two species are known to produce yessotoxins that are not considered a health risk for humans and are thus not discussed further in this report.

Diarrhetic Shellfish Poisoning DSP is the predo-minant threat to mussel farmers and consumers in Sweden. The phytoplankton species in Sweden that have been linked to DSP can be found within the Dinophysis genera, i.e. D. acuminata Claparède et Lachmann, D. acuta Ehrenberg, and to a minor extent D. norvegica Claparède et Lachmann and D. rotundata Claparède et Lachmann. The last species is heterotrophic and synonymous with Phalacroma rotundatum (Claparède et Lachmann) Kofoid et Michener 1911 while the others are mixotrophic organisms. Dinophysis spp are relatively large (ca 40-100 µm) planktonic organisms that occur year round in the area. Cell numbers are most often below 1000 cells.l-1_{(Fig. 9; Karlson et al. 2005).}

Warnings for toxin risk in blue mussels are issued at cell densities of 300 cells.l-1_{for D. acuta and at}

100 cells.l-1_{if occurring three weeks continuously.}

For D. acuminata the warning level is 900 cells.l-1_.

D. acuta in Skagerrak is a potent producer of both OA and DTX-1. D. acuminata from the region usually only produces OA although this species has been shown to be a producer of DTX-1 in other regions (Andersen et al. 1996). D. norvegica has never been proven to produce DST in the

Ska-Figure 7. Chemical structure of the causative agents of diarrhetic shellfish poisoning (DSP), okadaic acid and the dinophysistoxins.

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O% O% O% O. O. O. 2IKSGRØNSENNR +OSTERFJORDENNR "ROFJORDEN3TRETUDDEN $ANAFJORD ªSTOL 3TIGFJORDENYTTRE +OLJFJORD

3KAGERR

AK

+ATTEGATT

(AVSTENSFJORD "YFJORDEN 2ØVUNGARNA

Figure 8. Locations for quantitative phytoplankton monitoring from 1990 to 2003. Some locations have only been visited a short time, others are new and some others are finished. Yellow markers indicate stations still active in 2006 while stations with red markers have been discontinued. From Karlson et al. (2006).

gerrak region and D. rotundata usually occurs in low numbers and thus does not contribute to the problem. Most attempts to correlate occurrence of Dinophysis abundance and the concentration of DST in mussels have failed, except on short time-scales and at local sites (e.g. Godhe et al 2002). One explanation might be the considerable varia-tion of toxin content per Dinophysis cell. Another is the characteristic feature of Dinophysis blooms, the formation of dense patchy populations in thermo-clines or pycnothermo-clines.

Other planktonic organisms that may cause shell-fish toxicity do occur along the Bohus coast. In the genus Protoperidinium a few species have been shown to cause Azaspirazidic Shellfish Poisoning (AZP). No data on the toxins causing AZP in Swe-dish waters is known to the authors of this report.

Monitoring of phytoplankton

Routine algal monitoring is performed once a month at 10 stations along the coastline (see Fig. 8) by tube sampling at 0-10 m and 10-20 m. The algae are fixed by Lugol (Uthermöhl 1958) and examined using an inverted microscope at a magni-fication of 100 to 200.

Phytoplankton sampling and analyses of potentio-nally toxic species is performed weekly in har-vesting areas since 2001. Sampling is performed by personal from National Food Administration. Analyses are made by SMHI since 2004. The data has not been included in this report.

Monitoring of DST

The EC regulation for controlling DST in bival-ves is based on a mouse bioassay. This test has the advantage of detecting unknown toxins that might appear in the area. However, the mouse test is semiquantitative and not always satisfactory in terms of detectability, specificity, and reliability. Use of animals in shellfish monitoring program-mes has also become increasingly unacceptable in several EU countries for ethical reasons. Analyses by chemical methods have however other disadvan-tages. These include low ability in detecting new toxins and usually problems to obtain pure toxin standards needed in the tests. The surveillance of the DST concentrations in mussels in Sweden has been performed by HPLC (High Performance Liquid Chromatography) for 14 years (Haamer et

Figure 9. Toxic algae (Dinophysis spp.) -> suspen-sion feeder (Mytilus edulis) -> human.

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1992 1994 1996 1998 2000 2002 0 1 2 3 4 5 Log Cells l − 1 Dinophysis All stations 0−10 m All stations 0−10 m All stations 0−10 m All stations 0−10 m All stations 0−10 m All stations 0−10 m All stations 0−10 m All stations 0−10 m All stations 0−10 m 1992 1994 1996 1998 2000 2002 0 1 2 3 4 5 Log Cells l − 1 10−20 m 10−20 m 10−20 m 10−20 m 10−20 m 10−20 m 10−20 m 10−20 m 10−20 m

Jan Apr Jul Oct

0 1 2 3 4 5 Log Cells l − 1 0−10 m 0−10 m 0−10 m 0−10 m 0−10 m 0−10 m 0−10 m 0−10 m 0−10 m

Jan Apr Jul Oct

0 1 2 3 4 5 Log Cells l − 1 10−20 m 10−20 m 10−20 m 10−20 m 10−20 m 10−20 m 10−20 m 10−20 m 10−20 m

Jan Apr Jul Oct

0 1000 2000 3000 4000 Cells l − 1

Monthly median & 50% quartile 0−10 m

Jan Apr Jul Oct

0 1000 2000 3000 4000 Cells l − 1

Monthly median & 50% quartile 10−20 m

Figure 10. From Karlson, B., Edler, L., Skjevik, A.-T. och Claesson, S. (2005). Växtplankton vid Bohuskusten - förstudie till utvärdering av miljöövervakningsdata 1990-2003. SMHI rapport 2005-70, pp. 58. The two graphs on the top show the number of dinoflagellates of the genus Dinophysis per litre from 0-10 m depth (red) and 10-20 m (blue) respectively. The graphs on the left show seasonal variations from raw-data. To the right the same data is shown as median, + 75 % quartile and - 25 % quartile.

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al. 1999). From the middle of 2000 the analyses were transferred to a commercial company, Ana-lyCen Nordic AB, and the method of choice was subsequently changed to HPLC-MS (HPLC with Mass Spectrometrical detection). The National Food Administration administers the monitoring of harmful algae and algal toxins in shellfish as well as opening and closing of harvesting areas to make sure that mussels are safe to eat (Nordlander, 2006). The “Water Quality association of the Bo-hus Coast” as well as mussel farmers and research projects has funded the Swedish analyses. Starting in 2001 the sampling program has been co-ordi-nated and partly funded by the Swedish National Food Administration.

2. Material & methods

2.1 Description of collected data

For routine monitoring of DSP, 15 mussels, five from the upper (1 m), five from the middle (5 m), and five from the bottom (8 m) of the mus-sel culturing band, are collected and weighed after removal of the shells. The hepatopancreas is dissected and weighed separately for determination of the relative proportions, which can vary from 10-25 % and result in a total of 10-30 g hepato-pancreas (HP). On average three samples a week are analysed for each area. This can however change due to time of year and with toxin levels in the mussels since many data are obtained from analy-ses of samples from mussel farmers. OA has been regularly monitored since 1988, DTX-1 between 1992-2000 with the exception of 1996.

2.2 Analysis methods

2.2.1.Mouse bioassay

The mouse bioassay was the first test developed to monitor DSP toxins in shellfish extracts (Yasumoto et al. 1978) and this test is still widely used. The main principle of the bioassay is to inject shellfish extracts intraperitoneally into a mouse and moni-tor the reaction. Time of death is ideally related to the amount of toxin in the injected extract and the amount is calculated from a standard curve as mouse units (MU). MU are defined as amounts of toxin required to kill two to three 20 g mice in 24 hours, such that one MU corresponds to 4 µg OA, 3.2 µg DTX-1 and 5 µg DTX-3 (Yasumoto

et al. 1995). The limit for marketing of shellfish within EU is 160 µg OA.kg–1_{mussel meat. This}

corresponds to the detection limit for the mouse bioassay. Most Swedish mussels that are exported to the EU market are still analysed by the mouse bioassay.

2.2.2. Rat bioassay

The rat bioassay was the first test ever performed to monitor DSP toxins in shellfish (Kat, 1983). In this test the digestive glands (or hepatopancreas) of mussels were dissected from the mussels and fed to rats. The fecal pellets from the rats were thereafter examined and if the rats showed symptoms of diar-rhoea the test was considered positive. Rat tests were performed sporadically during 1988-2000 in Sweden on chemically negative mussel samples. 2.2.3. Analytical procedure by HPLC using PDAM

A modified instrumental method using HPLC with fluorescence detection according to Lee et al. was used between 1988-2000 (Lee et al. 1987). A detailed description of the method can be found in Rehnstam-Holm et al. (submitted). In this method derivatization with 9-anthryldiazomethane (ADAM) is used to convert the toxins to fluores-cent ester derivatives. Problems with the stability of this substance initiated the search for a new reagent, and 1-pyrenyldiazomethane (PDAM) was found to be a good alternative.

The hepatopancreas sample was homogenised and 1.0 g of the homogenate was further used in the analysis. The toxins were extracted in methanol, delipidized by extraction with petroleum ether, and further extracted with a chloroform:water mixture. The chloroform layer was evaporated to dryness and derivatizised with a PDAM solution in methanol-ethyl acetate. The derivatized sample was concentrated on a silica gel cartridge column and the sample was eluted using methanol in chloro-form. The elute was evaporated to dryness, and the residue was dissolved in methanol prior to HPLC analysis.

The samples were analysed using a reversed-phase column Kromasil 5 C18. The instrument was calibrated with 10 ng okadaic acid and 5 ng DTX-1, which corresponds to 2 respectively 1 µg g-1_{hepatopancreas sample. A standard sample}

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was prepared for calibration and derivatized in the same way as the samples. The recovery yield for okadaic acid was 92 % with a coefficient of varia-tion of 4,8%. The recovery yield for DTX-1 was 90 % with a coefficient of variation of 6.9 %. The detection limit was set to 10 µg OA or DST-1.kg-1

mussel meat.

2.2.4. Analytical procedure by HPLC-MS

From the middle of 2000 toxin analyses have been performed by a commercial company, AnalyCen AB in Lidköping by using HPLC-MS. The analyti-cal procedure follows that of Aase & Rogstad (Aase et al. 1997).

0.5 µg toxin was added to toxin free mussel hepat-opancreas homogenates during every analytical event and a recovery ranging between 70-120 % was accepted. The detection limit with this method was set to 30 µg toxin.kg-1_{mussel meat.}

3. Results

3.1 Collected data

On average three samples a week have been ana-lysed for each area. This has however varied with time of year, toxin levels in the mussels and cultur-ing area, since most data are obtained from ana-lyses of samples from mussel farmers. This means that on occasions with high or very low toxic levels, mussel farmers are less prone to send samples for analyses. Mussel cultivation areas have also been abandoned after long periods of high toxicity in favour of other, less problematic areas.

Algal monitoring samples are usually collected only once a month and at different locations compared to mussel samples (see Fig. 8).

3.2 Occurrence of Dinophysis spp. and its

correlation to toxicity in mussels

Dinophysis spp. can be observed in plankton samp-les all over the year in the region at fairly limited numbers, i.e. between 100-10 000 cells.l-1_{. A}

regu-lar pattern of Dinophysis numbers can be observed during the years (Fig. 9). Highest numbers occur in mid July and during this period the dominating species are D. acuminata and D. norvegica. An ad-ditional smaller peak can be observed in October. Here the dominant species are D. acuminata and

D. acuta. Dominant species as well as toxicity per cell are probably important factors influencing the toxicity accumulated in mussel tissue. Further cor-relation analyses are however not within the scope of this report and will be published elsewhere.

3.3 Temporal and spatial distribution of total DST

The long Swedish regular analysis of diarrhetic shellfish toxins (from 1988) in mussels along the Skagerrak coast is a unique quantitative dataset. Okadaic acid (OA) has been and still is the domi-nating DST, but DTX-1 and DTX-2 have occur-red occasionally. Regular analyses of DTX-2 started in late 2006 and is not included in this report. In the figures toxin values are given as µg DST (OA+DTX-1).kg-1_{mussel meat. The large data}

set shows a clear strong seasonal variation in DST concentrations. In i.e. typical year high levels of DST in mussel tissue occurs from August until Fe-bruary, while levels are normally low from March until July, a pattern that also can been observed for the mean monthly toxicity for all years and most regions. The amplitude of the peaks differs signi-ficantly between years. Years 1989 -1990, 1994 -1995, 1998 and 2000-2002 have been especially bad. In other years 1992, 1997, and 2005, low levels of toxin were recorded with few values above the maximum residue limit (Nordlander, 2006), i.e. 160 µg kg-1_{mussel meat. A summer peak can}

be observed in most areas in late June - end of July in 1989, 1991, 1993, 1995, and 1998 to 2004. The toxin values in the mussels were during these periods normally below the maximum residue limit, but the pattern was not persistent. In 2002 the summer peak, which reached as high as 1400 µg DTX.kg-1_{mussel meat, appeared through out}

the whole Skagerrak area and in some regions (i.e. Tjärnö Archipelago, Fig. 13-15), the mussels con-tinued to be toxic until early spring next year. See also the discussion where figures 83 and 84 show the whole data set.

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3.4. Kosterfjorden

Water body Inre N Kosterfjorden 585400-110400

Figure 13. The highest measured value each week is presented with a specific colour. 160 µg.kg-1_{is the}

regula-tory maximum residue limit.

There are only two measurements of DST from the water body Inre Kosterfjorden during the whole investigation period 1988 to 2004. These two are from 2002. The up-per graph shows DST values during all measured years. The graph in the middle shows the distribution of DST values during the seasonal month of the year. The bottom graph shows the same data in another way, where the highest measured value each week is presented with a specific colour. The blue and green colour shows DST values below the regulatory maximum residue limit.

Figure 11. All measurements of DST (µg.kg-1_{) in Kosterfjorden from 1988 to 2005.}

Figure 12. All measurements of DST (µg.kg-1_{) in Kosterfjorden from 1988 to 2005 presented during a year-scale.}

1988 1990 1992 1994 1996 1998 2000 2002 2004 2 4 6 8 10 12 14 16 18 20 22 24Week number 26 28 30 32 34 36 38 40 42 44 46 48 50 52 Year 0-80 µg/kg 81-160 µg/kg 161-320 µg/kg 321-640 µg/kg >641 µg/kg no measurements 19880 1989 1990 1991 1992 1993 1994 1995 1996 1997 1998 1999 2000 2001 2002 2003 2004 2005 500 1000 1500 2000 2500 DST, µ g kg −1

Jan Feb Mar Apr May Jun Jul Aug Sep Oct Nov Dec

0 500 1000 1500 2000 2500 DST, µ g kg −1

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3.5. Tjärnö archipelago

Water bodies Inre Tjärnöarkipelagen 585290-110830

and N Ytrre Tjärnöarkipelagen 585200-111140

The first mussel-culture in Sweden was established in 1971 in the Tjärnö archipelago neighbourhood. Regular sampling in the area started 1988 and has been more or less regular since then. The upper graph shows the variation of DST during all the measu-red years. Some of the years show very low values, even below the regulatory maximum residue limit (160 µg.kg-1_{), and some years very high levels. The highest level measured}

during the whole period was about 2000 µg.kg-1_{in winter 1993-1994. The graph in the}

middle shows the distribution of DST values during the year and the pattern clearly shows that high DST values are an autumn-winter problem. The same pattern is shown in the bottom graph but in another way. The highest measured value each week is presented with a specific colour. The blue and green colour shows DST values below the regulatory maximum residue limit.

Figure 14. All measurements of DST (µg.kg-1_{) in Tjärnö archipelago from 1988 to 2005.}

Figure 15. All measurements of DST (µg.kg-1_{) in Tjärnö archipelago from 1988 to 2005 presented during a}

year-scale. 1988 1990 1992 1994 1996 1998 2000 2002 2004 2 4 6 8 10 12 14 16 18 20 22 24Week number 26 28 30 32 34 36 38 40 42 44 46 48 50 52 Year 0-80 µg/kg 81-160 µg/kg 161-320 µg/kg 321-640 µg/kg >641 µg/kg no measurements 19880 1989 1990 1991 1992 1993 1994 1995 1996 1997 1998 1999 2000 2001 2002 2003 2004 2005 500 1000 1500 2000 2500 DST, µ g kg −1

0 500 1000 1500 2000 2500 DST, µ g kg −1

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3.6. Råssö-Resö archipelago

Water bodies Råssö-Resöfjorden sek name 584890-110950 and Stridsfjorden 584750-111185

Sampling in the area started regularly in 1988 and has been more or less regular since then. The upper graph shows the variation of DST during all the measured years. Some of the years show very low values, even below the regulatory maximum residue limit (160 µg.kg-1_{), and some year very high levels. The highest level measured during}

the whole period was higher than 2200 µg.kg-1_{in winter 1988-1989. The graph in the}

middle shows the distribution of DST values during the year and the pattern clearly shows that high DST values are an autumn-winter problem. The same pattern is shown in the bottom graph but in another way. The highest measured value each week is presented with a specific colour. The blue and green colour shows DST values below the regulatory maximum residue limit.

Figure 17. All measurements of DST (µg.kg-1_{) in Råssö-Resö archipelago from 1988 to 2005.}

Figure 18. All measurements of DST (µg.kg-1_{) in Råssö-Resö archipelago from 1988 to 2005 presented during a}

0 500 1000 1500 2000 2500 DST, µ g kg −1

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3.7. Sannäsfjorden

Water body Sannäsfjorden sek name 584450-111445

Sampling in Sannäsfjorden started regularly in 1994 and has been more or less regular since then. The upper graph shows the variation of DST during all the measured years. Some of the years show very low values, even below the regulatory maximum residue li-mit (160 µg.kg-1_{), and some year very high levels. The highest level measured during the}

whole period is just below 1500 µg.kg-1_{in winter 2000-2001. The graph in the middle}

shows the distribution of DST values during the seasonal month of the year and the pattern clearly shows that high DST values are an autumn-winter problem. The same pattern is shown in the bottom graph but in another way. The highest measured value each week is presented with a specific colour. The blue and green colour shows DST values below the regulatory maximum residue limit.

Figure 20. All measurements of DST (µg.kg-1_{) in Sannäsfjorden from 1988 to 2005.}

Figure 21. All measurements of DST (µg.kg-1_{) in Sannäsfjorden from 1988 to 2005 presented during a}

0 500 1000 1500 2000 2500 DST, µ g kg −1

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3.8. Fjällbacka archipelago

Water body Fjällbacka inre skärgård 583710-111535

Sampling in the area started regularly in 1988 and has been more or less regular since then. It was a gap in sampling from 1990 to 1994. The upper graph shows the variation of DST during all the measured years. Some of the years show very low values, even be-low the regulatory maximum residue limit (160 µg.kg-1_{), and some year very high levels.}

The highest level measured during the whole period is just below 1500 µg.kg-1_{in winter}

1994-1995. The graph in the middle shows the distribution of DST values during the seasonal month of the year and the pattern clearly shows that high DST values are an autumn-winter problem. The same pattern is shown in the bottom graph but in another way. The highest measured value each week is presented with a specific colour. The blue and green colour shows DST values below the regulatory maximum residue limit.

Figure 23. All measurements of DST (µg.kg-1_{) in Fjällbacka archipelago from 1988 to 2005.}

Figure 24. All measurements of DST (µg.kg-1_{) in Fjällbacka archipelago from 1988 to 2005 presented during a}

0 500 1000 1500 2000 2500 DST, µ g kg −1

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3.9. Sotefjorden

Water body Sotefjorden 582700-110451 585290-110830

Sampling in Sotefjorden started regularly in 2001. The upper graph shows the variation of DST during all the measured years. Some of the years show very low values, even below the regulatory maximum residue limit (160 µg.kg-1_{), and some year very high}

levels. The highest level measured is about 800 µg.kg-1_{in winter 2002-2003. The graph}

in the middle shows the distribution of DST values during the seasonal month of the year. The same pattern is shown in the bottom graph but in another way. The highest measured value each week is presented with a specific colour. The blue and green colour shows DST values below the regulatory maximum residue limit.

Figure 26. All measurements of DST (µg.kg-1_{) in Sotefjorden from 1988 to 2005.}

Figure 27. All measurements of DST (µg.kg-1_{) in Sotefjorden from 1988 to 2005 presented during a year-scale.}

0 500 1000 1500 2000 2500 DST, µ g kg −1

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3.10. Gullmarns centralbassäng

Water body Gullmarns centralbassäng 581700-113000

Sampling in the area started regularly in 1988 and has been more or less regular since then. The data from the Gullmar Fjord is not complete due to inconsistencies in the data set. There are also some concerns about the quality of the presented data for this area. The upper graph shows the variation of DST during all the measured years. Some of the years show very low values, even below the regulatory maximum residue limit (160 µg.kg-1_{), and some years very high levels. The highest level measured during the}

whole period was around 2400 µg.kg-1_{in winter 1988-1989. The graph in the middle}

shows the distribution of DST values during the seasonal month of the year and the pattern clearly shows that high DST values are an autumn-winter problem. The same pattern is shown in the bottom graph but in another way. The highest measured value each week is presented with a specific colour. The blue and green colour shows DST values below the regulatory maximum residue limit.

Figure 29. All measurements of DST (µg.kg-1_{) in Gullmarns centralbassäng from 1988 to 2005.}

Figure 30. All measurements of DST (µg.kg-1_{) in Gullmarns centralbassäng from 1988 to 2005 presented during}

a year-scale. 1988 1990 1992 1994 1996 1998 2000 2002 2004 2 4 6 8 10 12 14 16 18 20 22 24Week number 26 28 30 32 34 36 38 40 42 44 46 48 50 52 Year 0-80 µg/kg 81-160 µg/kg 161-320 µg/kg 321-640 µg/kg >641 µg/kg no measurements 1988 1989 1990 1991 1992 1993 1994 1995 1996 1997 1998 1999 2000 2001 2002 2003 2004 2005 0 500 1000 1500 2000 2500 DST, µ g kg −1

0 500 1000 1500 2000 2500 DST, µ g kg −1

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3.11. Malö strömmar

Water body Malö strömmar 581200-112960

There is only a short sampling period in Malö strömmar from 1995 to 1996. The upper graph shows the variation of DST during all the measured years. All values were below the regulatory maximum residue limit (160 µg.kg-1_{). The graph in the middle shows the}

distribution of DST values during the seasonal month of the year. In the bottom graph the highest measured value each week is presented with a specific colour. The blue and green colour shows DST values below the regulatory maximum residue limit.

Figure 32. All measurements of DST (µg.kg-1_{) in Malö strömmar from 1988 to 2005.}

Figure 33. All measurements of DST (µg.kg-1_{) in Malö strömmar from 1988 to 2005 presented during a}

0 500 1000 1500 2000 2500 DST, µ g kg −1

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3.12. Koljö fjord

Water body Koljö fjord 581260-113220

Sampling in Koljö fjord started regularly in 1990. The upper graph shows the variation of DST during all the measured years. Some of the years show very low values, even below the regulatory maximum residue limit (160 µg.kg-1_{), and some year very high}

levels. The highest level measured is about 2000 µg.kg-1_{in winter 2000-2001. Before}

autumn 1998 there were only two samplings above the regulatory maximum residue limit. After this period we have the same pattern as on other places along the west coast of Sweden. The graph in the middle shows the distribution of DST values during the seasonal month of the year and the pattern clearly shows that high DST values are an autumn-winter problem. The same pattern is shown in the bottom graph but in another way. The highest measured value each week is presented with a specific colour. The blue and green colour shows DST values below the regulatory maximum residue limit.

Figure 35. All measurements of DST (µg.kg-1_{) in Koljö fjord from 1988 to 2005.}

Figure 36. All measurements of DST (µg.kg-1_{) in Koljö fjord from 1988 to 2005 presented during a year-scale.}

0 500 1000 1500 2000 2500 DST, µ g kg −1

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3.13. Borgilefjorden

Water body Borgilefjorden 581520-113750

Sampling in Borgilefjorden started regularly in 2001. The upper graph shows the varia-tion of DST during all the measured years. The highest level measured is about 1500 µg.kg-1_{in autumn 2003. The graph in the middle shows the distribution of DST values}

during the seasonal month of the year. In the bottom graph the highest measured value each week is presented with a specific colour. The blue and green colour shows DST values below the regulatory maximum residue limit.

Figure 38. All measurements of DST (µg.kg-1_{) in Borgilefjorden from 1988 to 2005.}

Figure 39. All measurements of DST (µg.kg-1_{) in Borgilefjorden from 1988 to 2005 presented during a year-scale.}

0 500 1000 1500 2000 2500 DST, µg kg − 1

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3.14. Kalvöfjord

Water body Kalvöfjord 581540-114000

Sampling in Kalvöfjord started regularly in 2000. The upper graph shows the variation of DST during all the measured years. The highest level measured is just above 500 µg.kg-1_{in winter 2000. The graph in the middle shows the distribution of DST values}

during the seasonal month of the year. In the bottom graph the highest measured value each week is presented with a specific colour. The blue and green colour shows DST values below the regulatory maximum residue limit.

Figure 41. All measurements of DST (µg.kg-1_{) in Kalvöfjord from 1988 to 2005.}

Figure 42. All measurements of DST (µg.kg-1_{) in Kalvöfjord from 1988 to 2005 presented during a year-scale.}

0 500 1000 1500 2000 2500 DST, µ g kg −1

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3.15. Havstensfjorden

Water body Havstensfjorden 581740-114820

Sampling in Havstensfjorden started regularly in 1994. The upper graph shows the variation of DST during all the measured years. The highest level measured is around 1500 µg.kg-1_{in winter 1998-1999. The graph in the middle shows the distribution of}

DST values during the seasonal month of the year. In the bottom graph the highest measured value each week is presented with a specific colour. The blue and green colour shows DST values below the regulatory maximum residue limit.

Figure 44. All measurements of DST (µg.kg-1_{) in Havstensfjorden from 1988 to 2005.}

Figure 45. All measurements of DST (µg.kg-1_{) in Havstensfjorden from 1988 to 2005 presented during a}

0 500 1000 1500 2000 2500 DST, µ g kg −1

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3.16. Ljungskile

Water body Ljungskile 581260-115280

Sampling in Ljungskile started regularly in 1997. The upper graph shows the variation of DST during all the measured years. Some of the years show very low values, even below the regulatory maximum residue limit (160 µg.kg-1_{), and some year very high}

levels. The highest level measured is about 1400 µg.kg-1_{in winter 2000-2001. The graph}

in the middle shows the distribution of DST values during the seasonal month of the year and the pattern clearly shows that high DST values are an autumn-winter problem. The same pattern is shown in the bottom graph but in another way. The highest measu-red value each week is presented with a specific colour. The blue and green colour shows DST values below the regulatory maximum residue limit.

Figure 47. All measurements of DST (µg.kg-1_{) in Ljungskile from 1988 to 2005.}

Figure 48. All measurements of DST (µg.kg-1_{) in Ljungskile from 1988 to 2005 presented during a year-scale.}

0 500 1000 1500 2000 2500 DST, µ g kg −1

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3.17. Käringöfjorden

Water body Käringöfjorden 580550-112460

There is only one sample taken in Käringöfjorden and it is from 1999. The upper graph shows the variation of DST during all the measured years. The graph in the middle shows the distribution of DST values during the seasonal month of the year. In the bot-tom graph the highest measured value each week is presented with a specific colour. The blue and green colour shows DST values below the regulatory maximum residue limit.

Figure 50. All measurements of DST (µg.kg-1_{) in Käringöfjorden from 1988 to 2005.}

Figure 51. All measurements of DST (µg.kg-1_{) in Käringöfjorden from 1988 to 2005 presented during a}

0 500 1000 1500 2000 2500 DST, µ g kg −1

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3.18. Mollöfjorden

Water body Mollöfjorden 580240-112501

Sampling in Mollöfjorden started regularly in 1999. The upper graph shows the varia-tion of DST during all the measured years. The highest level measured is just below 1000 µg.kg-1_{in winter 1999-2000. The graph in the middle shows the distribution of}

DST values during the seasonal month of the year and the pattern shows that high DST values are an autumn-winter problem but high DST-values may also occur in June, July and August. The same pattern is shown in the bottom graph but in another way. The highest measured value each week is presented with a specific colour. The blue and green colour shows DST values below the regulatory maximum residue limit.

Figure 53. All measurements of DST (µg.kg-1_{) in Mollöfjorden from 1988 to 2005.}

Figure 54. All measurements of DST (µg.kg-1_{) in Mollöfjorden from 1988 to 2005 presented during a year-scale.}

0 500 1000 1500 2000 2500 DST, µ g kg −1

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3.19. Lyresund

Water body Lyresund 580500-112970

Sampling in Lyresund started regularly in 1995. The upper graph shows the variation of DST during all the measured years. The highest level measured is just above 1000 µg.kg-1_{in winter 2002-2003. The graph in the middle shows the distribution of DST}

values during the seasonal month of the year and the pattern clearly shows that high DST values are an autumn-winter problem. The same pattern is shown in the bottom graph but in another way. The highest measured value each week is presented with a specific colour. The blue and green colour shows DST values below the regulatory maxi-mum residue limit.

Figure 56. All measurements of DST (µg.kg-1_{) in Lyrösund from 1988 to 2005.}

Figure 57. All measurements of DST (µg.kg-1_{) in Lyrösund from 1988 to 2005 presented during a year-scale.}

0 500 1000 1500 2000 2500 DST, µ g kg −1

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3.20. Boxvike kile

Water body Boxvike kile 580650-113000

Sampling in Boxvike kile started regularly in 1988. The upper graph shows the varia-tion of DST during all the measured years. After 1994 is the data more sporadic. The highest level measured is just above 2000 µg.kg-1_{in winter 1989-1990. The graph in}

the middle shows the distribution of DST values during the seasonal month of the year and the pattern clearly shows that high DST values are an autumn-winter problem. The same pattern is shown in the bottom graph but in another way. The highest measured value each week is presented with a specific colour. The blue and green colour shows DST values below the regulatory maximum residue limit.

Figure 59. All measurements of DST (µg.kg-1_{) in Boxevike kile from 1988 to 2005.}

Figure 60. All measurements of DST (µg.kg-1_{) in Boxevike kile from 1988 to 2005 presented during a year-scale.}

0 500 1000 1500 2000 2500 DST, µ g kg −1

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3.21. Halsefjorden

Water body Halsefjorden 580688-114860

Sampling in Halsefjorden started regularly in 1989. The upper graph shows the varia-tion of DST during all the measured years. The highest level measured is around 2500 µg.kg-1_{in winter 1998-1999. The graph in the middle shows the distribution of DST}

va-lues during the seasonal month of the year and the pattern clearly shows that high DST values are an autumn-winter problem. The same pattern is shown in the bottom graph but in another way. The highest measured value each week is presented with a specific colour. The blue and green colour shows DST values below the regulatory maximum residue limit.

Figure 62. All measurements of DST (µg.kg-1_{) in Halsefjorden from 1988 to 2004.}

Figure 63. All measurements of DST (µg.kg-1_{) in Halsefjorden from 1988 to 2004 presented during a year-scale.}

0 500 1000 1500 2000 2500 DST, µ g kg −1

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3.22. Stigfjorden

Water body Stigfjorden 580325-113500

Sampling in Stigfjorden started regularly in 1996. The upper graph shows the variation of DST during all the measured years. The highest level measured is around 600 µg.kg-1

in winter 1999-2000 and 2002-2003. The graph in the middle shows the distribution of DST values during the seasonal month of the year and the pattern clearly shows that high DST values are an autumn-winter problem. The same pattern is shown in the bot-tom graph but in another way. The highest measured value each week is presented with a specific colour. The blue and green colour shows DST values below the regulatory maximum residue limit.

Figure 65. All measurements of DST (µg.kg-1_{) in Stigfjorden from 1988 to 2005.}

Figure 65. All measurements of DST (µg.kg-1_{) in Stigfjorden from 1988 to 2005 presented during a year-scale.}

0 500 1000 1500 2000 2500 DST, µ g kg −1

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3.23. Kalvöfjorden

Water body Kalvöfjorden 580610-113615

There are only three samples totally from Kalvöfjorden and they are from year 2000. The upper graph shows the variation of DST during all the measured years. The graph in the middle shows the distribution of DST values during the seasonal month of the year. In the bottom graph the highest measured value each week is presented with a specific colour. The blue and green colour shows DST values below the regulatory maxi-mum residue limit.

Figure 68. All measurements of DST (µg.kg-1_{) in Kalvöfjorden from 1988 to 2005.}

Figure 69. All measurements of DST (µg.kg-1_{) in Kalvöfjorden from 1988 to 2005 presented during a year-scale.}

0 500 1000 1500 2000 2500 DST, µ g kg −1

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3.24. Marstrandsfjorden

Water body Marstrandsfjorden 575340-113000

In Marstrandsfjorden there are only some samples from three different years, 2001, 2002 and 2004. The upper graph shows the variation of DST during all the measured years. The graph in the middle shows the distribution of DST values during the seaso-nal month of the year. In the bottom graph the highest measured value each week is presented with a specific colour. The blue and green colour shows DST values below the regulatory maximum residue limit.

Figure 71. All measurements of DST (µg.kg-1_{) in Marstrandsfjorden from 1988 to 2005.}

Figure 72. All measurements of DST (µg.kg-1_{) in Marstrandsfjorden from 1988 to 2005 presented during a}

year-scale. 1988 1990 1992 1994 1996 1998 2000 2002 2004 2 4 6 8 10 12 14 16 18 20 22 24Week number 26 28 30 32 34 36 38 40 42 44 46 48 50 52 Year 0-80 µg/kg 81-160 µg/kg 161-320 µg/kg 321-640 µg/kg >641 µg/kg no measurements 1988 1989 1990 1991 1992 1993 1994 1995 1996 1997 1998 1999 2000 2001 2002 2003 2004 2005 0 500 1000 1500 2000 2500 DST, µ g kg −1

0 500 1000 1500 2000 2500 DST, µ g kg −1

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3.25. Göteborgs s skärgårds kustvatten

Water body Göteborgs s skärgårds kustvatten 573300-113801

Sampling in Göteborgs s skärgårds kustvatten started regularly in 1991. The upper graph shows the variation of DST during all the measured years. The highest level mea-sured is from 1994 November to December with 5 values higher than 2500 and with the highest value in December on 4659 and around 1800 µg.kg-1_{in winter 1994-1995.}

The graph in the middle shows the distribution of DST values during the seasonal month of the year and the pattern clearly shows that high DST values are an autumn-winter problem. The same pattern is shown in the bottom graph but in another way. The highest measured value each week is presented with a specific colour. The blue and green colour shows DST values below the regulatory maximum residue limit.

Figure 74. All measurements of DST (µg.kg-1_{) in Göteborgs s skärgårds kustvatten from 1988 to 2005.}

Figure 75. All measurements of DST (µg.kg-1_{) in Göteborgs s skärgårds kustvatten from 1988 to 2005 presented}

during a year-scale. 1988 1990 1992 1994 1996 1998 2000 2002 2004 2 4 6 8 10 12 14 16 18 20 22 24Week number 26 28 30 32 34 36 38 40 42 44 46 48 50 52 Year 0-80 µg/kg 81-160 µg/kg 161-320 µg/kg 321-640 µg/kg >641 µg/kg no measurements 19880 1989 1990 1991 1992 1993 1994 1995 1996 1997 1998 1999 2000 2001 2002 2003 2004 2005 500 1000 1500 2000 2500 DST, µ g kg −1

0 500 1000 1500 2000 2500 DST, µ g kg −1

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3.26. Askims fjord

Water body Askims fjord 573500-115150

Sampling in Askims fjord started regularly in 1993. Most of the measurements have been performed in the summer periods. The upper graph shows the variation of DST during all the measured years. The graph in the middle shows the distribution of DST values during the seasonal month of the year. In the bottom graph the highest measured value each week is presented with a specific colour. The blue and green colour shows DST values below the regulatory maximum residue limit.

Figure 77. All measurements of DST (µg.kg-1_{) in Askims fjord from 1988 to 2005.}

Figure 78. All measurements of DST (µg.kg-1_{) in Askims fjord from 1988 to 2005 presented during a year-scale.}

0 500 1000 1500 2000 2500 DST, µ g kg −1

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3.27. N m Hallands kustvatten

Water body N m Hallands kustvatten 570000-120701

Sampling in N m Hallands kustvatten started in 1994 and finished in 1995. Most of the measurements have been performed in the summer periods. The upper graph shows the variation of DST during all the measured years. The graph in the middle shows the distribution of DST values during the seasonal month of the year. In the bottom graph the highest measured value each week is presented with a specific colour. The blue and green colour shows DST values below the regulatory maximum residue limit.

Figure 80. All measurements of DST (µg.kg-1_{) in N m Hallands kustvatten from 1988 to 2005.}

Figure 81. All measurements of DST (µg.kg-1_{) in N m Hallands kustvatten from 1988 to 2005 presented during a}

0 500 1000 1500 2000 2500 DST, µ g kg −1